Tom Hammond wrote:
Fellas:
There is NO(!) means of significantly re-calibrating the keyer speed...
I did say the adjustment range would be rather limited!
and it should not be off by nearly THAT much.
Sorry, I couldn't resist giving a literal reply. Yes, the keyer speed
is crystal controlled by the 4MHz clock crystal (which cannot be
significantly in error without an obvious failure of the VFO
calibration). If the speed is wrong, it is one of:
- a hardware fault in the microcontroller;
- a bug in coding the timer handling;
- a difference in the definition of speed between the firmware
coder and the user.
The Keyer speed control IS a POT... the ONLY encoder is the VFO knob.
Physically its a pot, but its function in the K2 is as a shaft encoder.
The microcontroller reads the position of the pot as, as a number, and
uses that number to decide how fast to send the morse. It is not being
used to control the R part of an RC time constant as might be the case
in a non-software implementation of a keyer. I'd therefore say it was a
poor man's encoder, rather than a pot, in reality.
C22 is the master oscillator calibration capacitor which sets the
calibration for the entire K2. If you adjust C22, you will HAVE to
re-run CAL PLL, and then you will probably want to re-run CAL FIL for
each of your XTAL filter settings.
If you were to to modify C22 to change the morse speed calibration,
which would be pretty pointless, as the adjustment range is probably
only about 100 parts per million, you *MUST NOT* re-run CAL PLL or CAL
FLTR. Both of these assume that C22 has been set to make the frequency
exactly 4MHz. (You also should not re-run these at a different
temperature from the one at which C22 was last correctly adjusted, if
you want maximum accuracy and you have the thermistor board.)
In normal operation, the 4MHz oscillator is not used as a frequency
reference, for anything except the morse speed. It is used as the
primary frequency reference during CAL PLL and CAL FLTR. As the normal
reason for adjusting C22 is to make the 4MHz more accurate, the natural
consequence of changing is that one would want to recalibrate the PLL
master reference oscillator, which is what sets the frequency reference
in normal operation, but is trimmed with an electrically, rather than
mechanically, variable capacitor. If one compromises its 4MHz accuracy
to achieve some other aim, it is no longer a good primary reference for
calibration.
PS I think the reply about individual calibration charts was also tongue
in cheek.
--
David Woolley
Emails are not formal business letters, whatever businesses may want.
RFC1855 says there should be an address here, but, in a world of spam,
that is no longer good advice, as archive address hiding may not work.
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